This invention relates to a switch assembly suitable for use in high power applications.
A conventional switch assembly includes first and second contacts, with one of the contacts movably mounted relative to the other. The first and second contacts are typically formed of the same material. The contacts are movable between a break position spaced from one another and a make position in electrical contact with one another. A switch assembly in perhaps its most simple form consists of a wall mounted switch for turning a lamp, or the like, on or off. With such a switch assembly, the first and second contacts are formed of a conductive material such as copper. Copper contacts are relatively inexpensive. Also, the copper contacts are suitable for low power applications of this type.
In industrial control applications, switch assemblies are used in various electrical devices such as control relays, contactors, motor starters and the like. These devices may be used in low power applications. However, these devices are often also used in so-called xe2x80x9chigh powerxe2x80x9d applications. The high power applications may be up to 600 VAC and rated for 60 amps. Copper is not generally used in these applications because the higher voltage drop and higher currents can cause overheating which can create relatively high strength tack-welds between the contacts.
Silver cadmium oxide has long been considered a very good material for high power switching applications. The silver provides good conductivity and has no non-conductive oxides. The anti-welding features of the cadmium oxide makes any tack welds brittle enough to break in the normal operation of the devices. However, silver cadmium oxide is a more expensive contact material than copper. Therefore, use of contacts solely of silver cadmium oxide can be costly.
Accordingly, there is a need for lower cost contacts for use in high power applications.
In accordance with the invention, a switch assembly includes a copper contact pad paired with a high power contact material contact pad.
Broadly, there is disclosed in accordance with a first aspect of the invention a switch assembly for use in an electrical apparatus including a first contact having a first substrate and a first contact pad. The first contact pad is of copper or of a copper alloy. A second contact has a second substrate and a second contact pad. The second contact pad is of silver or of a silver alloy. Means are provided for movably mounting the first contact relative to the second contact so that in a make position the first and second pads are in electrical contact with one another and in a break position the first and second contact pads are spaced from one another.
It is a feature of the invention that the first and second substrates may be selected from a group consisting of copper, brass and steel.
It is another feature of the invention that the first contact pad may comprise silver-plated copper.
It is still another feature of the invention that the second contact pad may be of a material selected from a group consisting of silver, silver cadmium oxide, silver tin oxide and silver nickel.
It is still another feature of the invention that the first contact pad may be integrally formed in the first substrate.
There is disclosed in accordance with another aspect of the invention a switch assembly for use in an electrical apparatus suitable for high power applications comprising a first contact having a first substrate and a first contact pad. The first contact pad is of copper or of a copper alloy. A second contact has a second substrate and a second contact pad. The second contact pad is of a high power contact material. Means are provided for movably mounting the first contact relative to the second contact so that in a make position the first and second contact pads are in electrical contact with one another and in a break position the first and second contact pads are spaced from one another.
It is a feature of the invention that the second contact pad may be of a material selected from a group consisting of silver, silver alloy, silver semi-refractory material, silver refractory material and tungsten.
It is disclosed in accordance with yet another aspect of the invention an electrical switch comprising a housing. A stationary contact is fixedly mounted in the housing and has a stationary substrate and a stationary contact pad. A movable contact has a movable substrate and a movable contact pad. The movable contact is movably mounted in the housing so that in a make position the stationary and movable contact pads are in electrical contact with one another and in a break position the stationary and movable contact pads are spaced from one another. One of the stationary contact pad and the movable contact pad is of copper or of a copper alloy, and the other of the stationary contact pad and the movable contact pad is of silver or of a silver alloy.
Further features and advantages of the invention will be readily apparent from the specification and from the drawings.